It has been hypothesized that ROS plays an important role in extracellular matrix/cartilage destruction in rheumatoid arthritis and may be responsible for the generation of agents that amplify inflammation as well. Inflammation is characterized by the recruitment of phagocytes from the blood stream, the adhesion of these cells to extracellular matrix (ECM) proteins, and the functional activation and secretion of microbicidal and cytotoxic products. However, our understanding of the interrelatedness of these processes is quite limited. Recent studies have shown that neutrophils and monocytes adhered to fibronectin and activated by inflammatory agents produce increased amounts of hydrogen peroxide. The applicants have recently demonstrated, by a specific quantitative method developed in their laboratory, that these cells also produce singlet oxygen. The production of ROS, particularly singlet oxygen, is an important part of the phagocyte arsenal against invading microorganisms, but is also involved in inflammation-related tissue destruction, in conjunction with proteolytic enzymes released by the activated cells. In rheumatoid arthritis, the recruitment of leukocytes from the circulation and increased synovial cell formation results in an increased loss of cartilage at these sites. It has been suggested that ROS are themselves involved in the process of cartilage destruction and that in addition to the recruited phagocytes, synovial cells may be capable of producing ROS when activated during inflammation. This proposal is thus divided into four general areas: (1) Biochemical quantification of the ROS, particularly singlet oxygen, produced by neutrophils, monocytes, and synovial cells, adhered to ECM proteins or cartilagenous surfaces and stimulated with inflammatory mediators; (2) cytochemical localization of ROS production sites in adherent cells and cell populations associated with articular cartilage; (3) biochemical identification of the oxygenase(s) or peroxidases involved in the production of the ROS, particularly singlet oxygen, using specific inhibitors and by preparing cell-free systems to determine the amount of NAD(P)H-oxidase or other oxidase activity these cells contain; and (4) assessment of the pathophysiological importance of the ROS, particularly singlet oxygen, in mediating ECM damage or in the production of inflammatory mediators by determining the direct effects of ROS on ECM proteins and articular cartilage as well as the susceptibility of the ROS-exposed ECM proteins and cartilage to proteolytic degradation.Information obtained from these studies, it is hoped, will add significantly to our understanding of the role ROS play in the pathophysiology of inflammation associated with rheumatoid arthritis.